The present invention pertains to a dynamic element matching method and device for use in a digital/analog converter (DAC) and other electronic devices.
Conventional DACs include the ΔΣ (delta-sigma) modulator type, which employs over-sampling. The characteristics of the ΔΣ modulator used in said DAC primarily depend on the operating frequency and the oversampling ratio. That is, as the oversampling ratio is increased, the quantization noise (the source of the out-of-band noise) decreases, and the noise-shaped bandwidth increases. Consequently, one may simply increase the over-sampling ratio of the ΔΣ modulator. On the other hand, for a high over-sampling ratio, the analog portion (especially the plural analog segments that function as weight generators of the DAC) requires a high operating frequency. However, if the operating frequency is too high, distortion will occur, and the distortion performance (THD performance) will deteriorate. As a result, there is a trade-off between the over-sampling ratio and the analog distortion.
In the ΔΣ modulator DAC of the prior art, a dynamic element matching (DEM) circuit is used (see Non -Patent References 1-3). In this DAC, the distortion of the an analog portion takes place due to high speed switching of the analog segment (it acts as a weight generator, and is also called the conversion element), and the switching of said analog segment mainly depends on the DEM circuit contained in the DAC. For the DEM circuit, in order to reduce the influence of mismatch between analog segments, that is, the influence of mismatch between weights generated for the various analog segments, the number of switching times for the analog segments is greatly increased. As a result, distortion of the analog portion rises.
For references, see, Tao Shui, Richard Schreier and Forrest Hudson, “Mismatch Shaping for a Current-Mode Multibit Delta-Sigma DAC,” IEEE Journal of Solid-State Circuits, Vol. 34, No. 3, Mar. 1999, pp. 331-338; R. Schreier and B. Zhang, “Noise-shaped Multibit D/A Convertor Employing Unit Elements,” Electronics Letters, 28th Sep. 1995, Vol. 31, No. 20, pp. 1712-1713; and Tao Shui, Richard Schreier and Forrest Hudson, “Modified “Mismatch-Shaping for Continuous Time Delta-Sigma Modulators,” IEEE 1998, Custom Integrated Circuits Conference, pp. 225-228.
Consequently, the purpose of the present invention is to provide an improved dynamic element matching (DEM) method and device.
Another purpose of the present invention is to provide a DAC or other electronic device adopting said DEM method or device.